Why do we sleep? Philosophers, neuroscientists and researchers have struggled with this seemingly simple question for centuries. Obviously it helps our body physically recuperate from a day’s worth of activities, labor and work. But what about our minds and emotional health? How does sleep affect those?

Now, a small group of neuroscientists is arguing that at least one vital function of sleep is bound up with learning and memory. A cascade of new findings, in animals and humans, suggest that sleep plays a critical role in flagging and storing important memories, both intellectual and physical, and perhaps in seeing subtle connections that were invisible during waking — a new way to solve a math or Easter egg problem, even an unseen pattern causing stress in a marriage.

The theory is controversial, and some scientists insist that it’s still far from clear whether the sleeping brain can do anything with memories that the waking brain doesn’t also do, in moments of quiet contemplation.

The key, however, is that sleep is perhaps a far more complicated phenomenon than we at first thought. We may not just be lying there, unconsciously dreaming, and doing nothing. Our brains may still be actively at work, making different connections than our conscious mind can.

This is a fascinating idea — it’ll be interesting to watch as the researchers pursue these hypotheses further.

Also yesterday saw the release of a study that showed a lack of sleep really messes with our emotions and thinking. Well, actually, anyone who’s ever gone through sleep deprivation already knew that, but now we have 26 pretty pictures from fMRI’s to “prove” it. Filed under “I can’t believe they fund studies like this.”

In the researchers’ defense, they claim, “Before, it was difficult to separate out the effect of sleep versus the [mental disorder] itself. Now we’re closer to being able to look into whether the person has a psychiatric disease or a sleep disorder.” I guess, but I still don’t see an fMRI being used as a diagnostic tool in this area any time soon.

Dr. John Grohol is the founder & CEO of Psych Central. He is an author, researcher and expert in mental health online, and has been writing about online behavior, mental health and psychology issues -- as well as the intersection of technology and human behavior -- since 1992. Dr. Grohol sits on the editorial board of the journal Cyberpsychology, Behavior and Social Networking and is a founding board member and treasurer of the Society for Participatory Medicine.